1. Field of the Invention
The present invention relates to a fabrication method for fabricating an electron source substrate comprising an array of multiple electron emission devices each having a pair of device electrodes and an electroconductive thin film connecting the device electrodes, with a electron emission portion formed on the electroconductive thin film and a substrate.
2. Description of the Related Art
An electron source substrate is a substrate used for a display, comprising an array of multiple electron emission devices each having a pair of device electrodes on an insulating substrate and an electroconductive thin film connecting the device electrodes, with an electron emission portion formed on the electroconductive thin film, and particularly involve surface-conduction-type electron-emitting devices as electron sources.
Conventionally, two general types of electron-emitting devices are known; thermionic emitters and cold-cathode emitters. There are different types of the cold-cathode emitters, such as electron emission types (hereafter referred to as “FE type”), metal-insulating-metal types (hereafter referred to as “MIM type”), surface-conduction-type electron-emitting devices, and so forth.
Known examples of an FE type include that disclosed by W. P, Dyke & W. W. Dolan in “Field Emission”, Advance in Electron Physics, 8, 89 (1956), and C. A. Spindt in “Physical Properties of Thin-Film Field Emission Cathodes with Molybdenum Cones”, J. Appl. Phys 47, 5248 (1976).
On the other hand, as for MIM types, that disclosed by C. A. Mead in “Operation of Tunnel-Emission Devices” J. Appl. Phys., 32, 646 (1961) is known.
Further, known examples of a surface-conduction-type electron-emitting device include that disclosed by M. I. Elinson in “Radio Eng. Electron Phys., 10, 1290” (1965), and so forth. A surface-conduction-type electron-emitting device takes advantage of a phenomenon wherein electron emission is generated by applying a current to a small-area thin film formed on a substrate, the current being applied in parallel to the face of the film. Reported examples of such surface-conduction-type electron-emitting devices include those using a SnO2 thin film (Elinson et al), this using Au thin film (G. Dittmer, “Thin Solid Films”, 9, 317 (1972)), those using In2O3/SnO2 thin film (M. Hartwell and C. G Fonstad “IEEE Trans. ED Conf.”, 519 (1975)), those using carbon thin film (Hisashi Araki et al. “Journal of the Vacuum Society of Japan”, vol. 26, No. 1, p. 22 (1983)), and so forth.
FIG. 5 shows a typical example of the surface-conduction electron-emitting device, according to M. Hartwell described above. In the figure, reference numeral 11 denotes a glass substrate, and 12 and 13 denote a pair of device electrodes formed so as to face each other on the glass substrate. Reference numeral 14 denotes an electroconductive thin film of a metal oxide thin film which has been formed in an H-shaped pattern by sputtering or the like, and an electron emission portion 15 formed by an electrification process called “energization forming”. Spacing L between the device electrodes of the surface-conduction electron-emitting device is set between 0.5 to 1 mm, and the width W thereof is set to 0.1 mm. The position and shape of the electron emission portion 15 is represented schematically, since the position and shape thereof is indeterminant.
A method of producing a surface-conduction electron-emitting device, wherein a liquid containing an electroconductive thin-film material applied in the form of a droplet is provided between a pair of electrodes, the condition of providing the droplet between the electrodes is detected, and the droplet is provided between the electrodes based on the information obtained regarding the condition of providing, is disclosed as an inexpensive and simple method for producing an electron source substrate (EP717428A, corresponding Japanese Patent Laid-Open No. 9-69334).
Also disclosed is a method for forming a plurality of electroconductive films electrically connected to a common line, comprising: a step for detecting the displacement condition of the common line or a member accessory to the common line; a step for calculating positional information concerning a plurality of locations where electroconductive film material is to be provided to be electrically connected to the common line based on the results of the detection; and a step for providing the electroconductive film material at the plurality of locations, based on the positional information (EP936652A, corresponding Japanese Patent Laid-Open No. 2000-251665).
However, as the size of the area where droplets are provided increases along with the size of the substrate increasing, it becomes extremely difficult to maintain the overall positional precision of the electrodes on the entire substrate (or substitutes thereof) at a level the same as with smaller-sized substrates, i.e., to keep the distortion at the same level, and also, precision regarding irregularities in the thickness of the substrate tends to deteriorate. Accordingly, there is a need to increase the number of measurement points to measure the position of the device electrodes as compared to conventional arrangements in order to provide the precise discharging of droplets to all device electrode positions on the substrate.
Also, there is a need to repeat the action of moving and positioning the substrate so that the device electrode pattern is in the field of view of a measurement optical system, and then control the position of the substrate within the focal range of the optical system to measure the pattern position, for each of the measurement points. This means an increase in the number of measurement points results in a proportionate increase in the amount of time necessary to measure the multiple device electrodes.